The collar and the hem are in correct body groups. For example the collar is in chest body group. Just in a different mat zone (trims). I think the issue is the hem and the collar and the caps on the sleeves are loose and not attached to the for a lack of a better word the dress. In other words there are no verts of the collar attached the dress. That is why it falls during the sim.

Gary

"Those who lose themselves in a passion lose less than those who lose their passion"